The present invention relates to the field of photomultiplier tubes, and more specifically to an optically powered photomultiplier tube.
Photomultiplier tubes are sensitive optical detection devices which are used for spectroscopy, pollution monitoring, scintillation detectors, and other applications requiring high sensitivity light detection.
A photomultiplier tube is a vacuum tube device that includes a photocathode which receives incident optical radiation and emits electrons. A photomultiplier tube also has stages of electrodes, or dynodes, that are biased so that electrons from the stages are serially accelerated to energies of 100 to 10,000 electron volts prior to impact on any given dynode stage. An anode collects the electrons which are emitted and multiplied in the photomultipier tube and conducted by a feedthrough out of the vacuum tube. A separate high voltage potential is required for the photocathode and for each dynode. The anode is typically at or near ground potential.
A major difficulty in using photomultiplier tubes pertains to high voltage potentials which must be provided to the dynodes. One approach uses a single high voltage supply and a series of resistors to divide the supply voltage to the separate voltage levels required for each dynode stage. This is an inconvenient solution because power is wasted. Use of a separated high voltage supply to each dynode is another way, but this requires several high voltage leads from the power supply to the photomultiplier tube. Another problem with these methods is that any current leakage from the high voltage contacts to the anode signal output may interfere with signal detection. Another difficulty with photomultiplier tubes is that several electrodes must pass through the body of the vacuum tube, providing opportunity for leakage currents. Further, the high voltage cables necessary to provide power to a conventional photomultiplier tube are sometimes inconvenient to route from a power supply to the location where it is desired to use the photomultiplier tube. Therefore, there is a need for a photomultiplier tube which does not require an external high voltage power source.